Understanding Chiari malformation

What is a Chiari malformation?

You probably are aware of the astonishing power of your brain and its role in controlling all of your bodily functions. However, you may be less familiar with your brain's anatomy and what each area of the brain is responsible for.

The brain is comprised of three main parts: the cerebrum, cerebellum and brain stem. The cerebellum is located at the lower back of the brain, near the base of the skull, and is responsible for functions including movement, balance and reflexes. The brain stem is a bundle of nerves that connect your brain and spinal cord. It is located at the base of the brain, and controls functions including breathing, heart rate, blood pressure and body temperature.

In normal, healthy individuals the skull is large enough to accommodate the brain, and the two fit perfectly together. But in some cases — often due to a structural defect present at birth — the brain does not fit inside the skull properly. Instead, parts of the brain (including the cerebellum and brain stem) may be squeezed down into the spinal canal, causing a number of medical problems.

This defect is formally known as a Chiari malformation, or Arnold-Chiari malformation.

Types of Chiari malformations

There are different types of Chiari malformations. They fall into one of four categories based on severity and which parts of the brain are pushed into the spinal canal:

• In Chiari malformation type I, only the lower part of the cerebellum has entered the spinal canal. It usually develops throughout childhood and adolescence, as the brain and skull continue to grow to adult size. For that reason, symptoms often do not appear until adolescence or adulthood (and some people never experience symptoms).
• In Chiari malformation type II, parts of both the cerebellum and brain stem protrude into the spinal canal. Type II is already present at birth, and is usually accompanied by a medical condition called myelomeningocele, which means the backbone and spinal canal did not close properly during fetal development. This type of Chiari malformation can be detected with a routine ultrasound exam during pregnancy, although it sometimes is not diagnosed until infancy or early childhood.
• Chiari malformation type III is not as common as types I and II, but it is the most severe form. In type III, the cerebellum and brain stem protrude into both the spinal canal and into the spinal cord. Babies born with type III also may have an abnormal opening in the back of their skull. This type of Chiari malformation is usually detected during a pregnancy ultrasound, or diagnosed soon after birth. It produces severe neurological symptoms and can cause death.
• Chiari malformation type IV is rare, and occurs in babies born with an incomplete or underdeveloped cerebellum. It is usually fatal during infancy.

While most types of Chiari malformation are due to a defect that occurs during fetal development (sometimes referred to as primary Chiari malformation), in rare cases people can acquire type I later in life. This is known as secondary or acquired Chiari malformation, and can result from several factors including:

• medical conditions that develop and take up space in the skull, including brain tumors
• medical conditions that increase pressure in the brain, including hydrocephalus and intracranial hypertension
• upper spine abnormalities, such as a condition called basilar invagination
• excess leaking of the fluid that surrounds the brain and spinal cord (called cerebrospinal fluid), caused by injury, infection or prolonged use of a medical device called a shunt

What are the symptoms of a Chiari malformation?

Signs and symptoms of Chiari malformations vary greatly, because each of the four types affect different portions of the brain and represent different degrees of severity. People with type I may not experience symptoms until adulthood, if at all, while types II and III cause different symptoms at a much younger age.

Among children and adults with type I, symptoms may include:

• severe headaches, especially near the base of the skull, that tend to appear or get worse after coughing, sneezing or straining
• neck pain
• vision problems including blurred or double vision, sensitivity to light and involuntary eye movements (a condition called nystagmus)
• ringing in the ears (a condition called tinnitus)
• balance problems
• dizziness or vertigo
• trouble with fine motor skills, including hand coordination
• numbness or tingling in the hands and feet
• muscle weakness
• difficulty speaking or swallowing

Babies or children with type II may experience the same symptoms associated with type I, as well as one or more of the following:

• gagging
• weak arms
• quick downward eye movements
• changes in breathing pattern, including brief periods where breathing pauses

If the medical condition known as myelomeningocele is also present with type II, symptoms may include partial or complete paralysis below the waist, and lack of bladder or bowel control.

Babies or children with type III may experience the same symptoms associated with type II, as well as additional, severe neurological symptoms that cause life-threatening complications. Type III is associated with a high infant mortality rate.

Due to the lack of proper brain development associated with type IV, most babies born with this abnormality do not survive.

Additional complications associated with Chiari malformations

Some children and adults with a Chiari malformation may develop additional, related medical conditions that affect the brain or spinal cord. These complications include:

• Hydrocephalus is caused by an excessive build-up of cerebrospinal fluid in the brain, causing dangerous pressure within the head. Although hydrocephalus can occur with any type of Chiari malformation, it is most commonly associated with type II.
• Spina bifida is a type of birth defect in which the spinal cord or its protective covering doesn't form properly, leaving portions of the spinal cord exposed. Children born with Chiari malformation type II often have the most severe form of spinal bifida, called myelomeningocele, which can cause paralysis.
• Syringomyelia is a medical condition that causes cysts filled with cerebrospinal fluid to form within the spinal cord. If the cysts grow, they can cause a variety of symptoms including pain, weakness and stiffness in the back, shoulders, arms or legs.
• Spinal curvature, including scoliosis (where the spine curves to the left or right) and kyphosis (where the spine bends significantly forward), is most common among children with Chiari malformation type 1.
• Tethered cord syndrome occurs when the spinal cord attaches itself to the spine, causing the cord to stretch. This abnormal stretching can lead to nerve and muscle damage below the waist.

Given the health risks associated with Chiari malformations, including these complex and often serious complications, it is important to seek care from physicians who have extensive experience diagnosing and treating them.

How are Chiari malformations diagnosed?

If your doctor suspects you or your child has a Chiari malformation, he or she will perform a combination of some of the following tests:

• A physical or neurological exam allows your doctor to check your eyes, hearing, balance, reflexes, strength, coordination and other functions controlled by the brain or spinal cord.
• An X-ray is a common imaging test that captures pictures of dense structures inside the body, including bones. An X-ray of the head and neck can help identify bone abnormalities associated with Chiari malformations.
• A computerized tomography (CT) scan may be used to capture two-dimensional, cross-sectional images of the brain and skull. It can help detect bone abnormalities as well as certain complications including hydrocephalus.
• A magnetic resonance imaging (MRI) scan captures 3-D images of the body. It is often used to diagnose Chiari malformation because it can provide detailed images of the cerebellum and brain stem, including whether they are protruding into the spinal canal.

How are Chiari malformations treated?

If your doctor confirms you or your child has a Chiari malformation, he or she will determine whether to treat you right away or to monitor your condition over time. Your doctor will weigh several important factors, including what type of Chiari malformation you have, the severity of your symptoms and your overall health.

Because treatment usually requires surgery (which involves risks of its own), if you do not have any symptoms your doctor may recommend ongoing monitoring, including repeat physical exams and MRI scans.

Although you may be able to manage some symptoms such as headaches and other types of mild pain using medication, surgery is the only option for people with debilitating symptoms. A variety of surgical procedures may be used, depending on your specific symptoms and whether you have additional complications that also need to be treated.

• Posterior fossa decompression is the most common surgery used to treat Chiari malformations. During the procedure, a neurosurgeon removes a small piece of bone from the back of the skull. This creates more space for the cerebellum and helps relieve pressure on the spinal canal.
• Spinal laminectomy may be performed to increase the size of the spinal canal and relieve pressure on the spinal cord. During the procedure, a bony portion of the spinal canal (called the lamina) is surgically removed.
• Duraplasty is used to enlarge the dura mater, which is the tough outer membrane that covers the brain. During the procedure, a neurosurgeon cuts open the dura mater and sews in a patch made of human tissue or an artificial material. The patch helps increase the size of the dura mater, providing more room for the brain and cerebrospinal fluid.
• Complications such as hydrocephalus and syringomyelia may be treated with a surgical procedure called shunting, which diverts and drains excess cerebrospinal fluid to another part of the body.
• Children with myelomeningocele may need surgery to close the opening in their spinal canal or reposition their spinal cord.

Chiari malformation care at Lyerly Neurosurgery

Since Lyerly Neurosurgery was founded in 1934, our physicians have cared for thousands of people who need treatment for a brain or spine condition.

Today our practice continues to build upon a legacy that blends compassion, safety and innovation. In partnership with Baptist Medical Center Jacksonville, our brain and spine surgeons routinely collaborate with other physicians to help care for patients with Chiari malformation.

Our team has the advanced tools, training and experience necessary to surgically treat adults with Chiari malformations and any related complications, including hydrocephalus, tethered cord syndrome and syringomyelia.